Pretreatment of hydroforming catalysts



May 5, 1959 W. F. JOHNSTON, JR PRETREATMENT OF HYDROFORMING CATALYSTS 2Sheets-Sheet 1- 8 Ew mafi a QR 8m sum 8w QQ Q9 an vm M m X, mm w l W- 3l o v M Q/ mm m V Q I I. g d I m N9 Filed March 9, 1954 WEAM ATTORNEYMay 5, 1959 Filed March 9, 1954 W. FQJOHNSTON, JR PRETRE ZATMENT OFHYDROFORMING CATALYSTS 2 Sheets-Shegat 2 0:47:41. Ysr ACT/WT) osauA/s/?A TE, F/ unifs per /00 hours CATALYST //VLE T TEMPERATURE, "F

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ATTORNEY United States Patent PRETREATMENT OF HYDROFORMING CATALYSTSWalker F. Johnston, Jr., La Marque, Tex., assignor to The American OilCompany Application March 9, 1954, Serial No. 414,954 7 Claims. (Cl.208-138) This invention relates to the reforming of hydrocarbons. Moreparticularly, it relates to the hydroforming of petroleum naphthas inthe presence of an aluminasupported platinum catalyst.

Within recent years, platinum-alumina catalysts have been adopted widelyfor upgrading petroleum naphthas into gasoline products of high octanenumber and improved performance characteristics, and for this purposesuch catalysts have a number of properties which have made themoutstandingly successful. They are capable of producing a product ofhigh octane number and desirable volatility characteristics in excellentyield over a long period of time, when employed with due regard to theWell known sensitivity of platinum metals to poisoning by various tracecomponents in the charging stocks. It is normal for such catalysts toproduce a product of very high octane number during the initial hours ofoperation, but the octane number ordinarily undergoes a more or lesssteady decline, depending upon a number of the operating variables,primarily the temperature, pressure, charging stock end-point, andconcentration of deleterious substances such as sulfur, arsenic, and thelike in the charging stock. It has been observed, moreover, that at thehigh hydroforming temperatures which are normally required to obtaingasolines of premium octane number, all of the various deleteriouseffects are emphasized, producing a higher rate of octane decline andmaking it correspondingly difficult to produce a reformate pool havingthe desired octane level. To avoid this difliculty, I have nowdiscovered a technique of operation whereby the octane number declinerate for platinum-alumina catalysts can be substantially lowered duringoperation at higher octane levels. It is accordingly an object of myinvention to improve the reforming of hydrocarbons, in particular thehydroforming of petroleum naphthas in the presence of alumina-supportedplatinum catalysts. A further object is to increase the reformate pooloctane number obtainable with platinumalumina catalysts. Another objectis to extend the elfective life of platinum-alumina hydroformingcatalysts. These and other objects of my invention will be apparent fromthe appended description and claims.

I have discovered that the overall performance of a platinum-aluminacatalyst in a hydroforming process for producing a premium-gradegasoline can be greatly improved by subjecting the catalyst to apreliminary conditioning for a period of around 10 to 100 hours or morein a hydroforming operation at a lower temperature from about to 75 F.,preferably from 25 to 50 F., below the temperature level initially to beemployed to reach the desired octane level, the other operatingconditions being within the conventional ranges. Following the saidpreconditioning period, the catalyst-zone temperature is raised directlyto the desired hydroforming level, and the catalyst is then found to besubstantially improved in activity maintenance, exhibiting a rate ofdecline in product. octane number below the decline rate of untreatedcatalysts.

materially temperature cycle.

My invention is especially useful in connection with the treatment ofnaphthenic-type naphthas to produce gasoline products having F-l octanenumbers in the range of to 100 or higher. In order to reach this levelof product quality, the hydroforming operation is best carried out at apressure within the range of about 100 to 500 pounds per square inchgage, a temperature between about 875 and 1000 F., preferably betweenabout 940 and 975 F., an hourly weight space velocity between about 0.5and 5, and a hydrogen input rate between about 2000 and 10,000 standardcubic feet per barrel of charging stock. I have succeeded in maintainingthe product pool octane level around during an extended period ofoperation by subjecting the catalyst to a preliminary exposure to ahydrocarbon stock under the defined conditions with the exception that alower temperature is employed which initially yields a hydroformatequality from 2 to 10 F-1 octane units below the maximum level thereafterafiorded by the catalyst. The pretreatment is preferably carried out ata substantially constant temperature ranging between about 800 and 950F., and preferably under temperature conditions which do not produce arise in product octane level during the pretreating operation.

The hydrocarbon stock employed in my catalyst pretreating step cansuitably be the petroleum naphtha subsequently to be employed in thehydroforming operation. Alternatively it can be another petroleumfraction of naphtha boiling range or a fraction thereof, or ahydroformed naphtha or a fraction thereof, or a mixture of suchmaterials. The charging stock should have an ASTM boiling range endpoint below about 425 F., preferably below about 375 F., and should below in sulfur (less than about 0.05 weight-percent) and othercontaminants. Parafiin and aromatic hydrocarbon diluents can be added ifdesired.

The application of my new technique is conveniently illustrated inconnection With the treatment of a conventional naphthenic naphthacontaining 40 to 60% naphthenes. When such a naphtha is hydroformed overa 0.6% platinum-on-alumina catalyst, a temperature of about 955 F. isinitially required at a pressure of 300 p.s.i.g. and an hourly weightspace velocity around 1.5 to produce a reformate having a clear F-loctane number around 100, and at this temperature the catalyst normallydeclines in activity at the rate of 4 octane numbers per hours onstream. By pretreating the catalyst in the said hydroforming operationat a lower temperature around 920 F. for 80 hours, and thereafterraising the temperature directly to the desired level of 955 F., theactivity decline of the catalyst during the subsequent operation isreduced to only 1.0 octane number per 100 hours. As a result, even afterallowance for the comparatively low octane number of the productobtained during the pretreatment period, the total prod uct output has asubstantially higher average octane level than is obtainable with any ofthe processes of the prior art.

The effectiveness of my new technique will be apparent by inspection ofthe attached graphs.

Figure 1 contains three curves, in which hydroformer product F-l clearoctane number is plotted against onstream time, the data having beenobtained from three platinum hydroforming tests under comparableconditions which dilfered significantly only with respect to the All ofthe tests were carried out at 300 pounds per square inch gage reactorpressure and a hydrogen input rate of 5,000 standard cubic feet perbarrel of feed over a 0.6% platinum-on-alumina catalyst. The chargingstock was a paraflinic heavy naphtha havgravity of 50.8 degrees, a Reidvapor pressure of 1.0

pound per square inch, and an F-l clear octane number of 44.8.

Curve A represents a first start-up hydroforming operation of theconventional type in a two-bed reaction system having an impressedtemperature gradient in each of the catalyst zones, simulating adiabaticoperation. At the beginning of the test, an average catalyst temperatureof 950 F. was established in the two zones, and the charging stock wasintroduced at an hourly weight space velocity of 1.0. Within five hours,a 100 F. temperature gradient had been established in each of the twozones, with catalyst inlet and outlet temperatures of 970 and 870 F.respectively. Under these conditions, it was observed that the productoctane number dropped off at the rate of 2 units per 100 hours.

Curve B represents a slow start-up hydroforming operation in which thehydroforming was begun at a low temperature and the temperature wasgradually raised to the desired operating level. This procedure ofraising the reactor temperature to compensate for loss in activityby thecatalyst is typical of the prior art, and is based on the well-knownobservation that the hydroforming effectiveness of a platinum-aluminacatalyst, measured in terms of reformate octane number, increases as thehydroforming temperature is raised. The test to which curve B relateswas also carried out in a two-bed impressed-gradient reaction system.The flow of charging stock was started at an hourly weight spacevelocity of 1.5 and with catalyst inlet and outlet temperatures of 800and 700 F. respectively in each of the two beds. The temperatures inboth beds were raised 5 F. per hour until inlet and outlet temperaturesof 950 and 850 F. were reached. The space velocity was then reduced to1.0 after a total of 40 hours on stream. Temperatures were thereafterraised gradually until the 100-octane level was reached at inlet andoutlet temperatures of 970 and 870 F. after a total of 110 hours onstream. At this point the temperature was held constant, and it wasobserved that the product quality declined at the rate of 1.7 octanenumbers per 100 hours.

Curve C represents the results of a test on my new process in asingle-bed quasi-isothermal reactor, operating at an hourly weight spacevelocity of 1.5. The catalyst inlet temperature was maintained at about920 F. for the first 80 hours on stream, and was thereafter raisedquickly to 970 F. (equivalent to an integrated average temperature of955 F. over the length of the catalyst bed), where it was held constant.During the initial lowtemperature period, the activity decline rate was2.5 octane numbers per 100 hours, but in the subsequenthigher-temperature operation, the decline rate was only 0.8 unit per 100hours, and was maintained at this level over an extended period ofoperation.

For further comparison, Figure 2 is a correlation of catalyst activitydecline rate against catalyst inlet temperature in a fixed-temperaturehydroforming operation of the prior-art type, employing a 0.6%platinum-on-alumina catalyst in the treatment of a paraffiuic heavynaphtha at 300 pounds per square inch gage, an hourly weight spacevelocity of 1.5, and a hydrogen input rate of 5,000 standard cubic feetper barrel of feed. The catalyst activity decline rate, it will beobserved, increases very rapidly with the temperature in the usualoperating range; and in all cases, it is substantially greater than therates obtainable by means of my invention. For instance, Figure 2indicates that a decline rate of 4.0 F-l units per 100 hours wouldnormally be expected under the defined conditions at a catalyst inlettemperature of 955 F., whereas I have observed a decline rate of only1.0 unit per 100 hours in an operation initiated at a relatively lowtemperature level according to my new technique.

In designating the temperature of a fixed-bed or moving-bed hydroformercatalyst zone, it is necessary to take into consideration the nature ofthe reactions involved in the hydroforming process. The most common anddesirable charging stocks are rich in naphthenes, which undergodehydrogenation toaromatics, a highly endothermic reaction. At theopposite extreme are the low-naphthene, parafiin-rich stocks, in whichexothermic hydrocracking reactions may predominate. As a result it isseldom that the combined reactions are isenthalpic, and it is ordinarilyfound that a temperature gradient of some magnitude exists innonfiuidized catalyst beds, even in reactors equipped with internalheat-exchange means. In adiabatic-type reactors, a temperature drop ofto F. through a single catalyst bed is commonly encountered whenprocessing naphthenic stocks. For this reason, it is necessary to employa consistent basis in designating the temperatures employed in thecatalyst pretreating step of my invention and in the subsequenthydroforming step at higher temperature. Thus, it is satisfactory tochoose the catalyst inlet temperature, or in general the temperature ofany point within the catalyst bed, provided that the same referencepoint is used in each step. It is also satisfactory to employ an averagecatalyst temperature, preferably an integrated average temperature overthe entire length of the catalyst bed.

Advantageous results are in general obtained from the pretreating stepof my invention without regard to the temperature pattern in thecatalyst zone. It will be apparent, however, that in zones having asteep temperature drop, the parts of the catalyst bed having abnormallylow temperatures (i.e., below about 800 F.) during the pretreatingoperation will receive less than the optimum degree of preconditioning.For this reason, it is desirable to minimize the temperature gradient,at least to the point of maintaining a minimum temperature in thecatalyst bed of at least about 800 F. Best results are obtained bymaintaining the catalyst zone at a uniform temperature throughout.

A convenient technique for minimizing the catalystzone temperaturegradient in my pretreating step, and thereby improving the effectivenessof the catalyst preconditioning, lies in choosing the charging stockand/or adjusting the charging-stock composition to hold the heat effectsduring the said step at as low a level as possible. In the temperaturerange employed, exothermic reactions such as hydrocracking do not takeplace to any important extent. The observed heat effects are largelycaused by the highly endothermic dehydrogenation of naphthenes toaromatics. It is accordingly advantageous to employ as the chargingstock in the pretreating step a stock low in naphthenes, such as aparafiinic naphtha, containing 20 percent or less of naphthenes, or todilute the regular hydroformer charging stock with 50 percent or more ofsuch a naphtha. We prefer to carry out the catalyst preconditioning withhydroformate (i.e., a stock which has already been hydroformed and whichconsequently shows little or no thermal eflect), or with a regularcharging stock diluted with 50 to 90 percent of hydroformate. It will beapparent that dilferent charging stocks may be used in the pretreatingand hydroforming operations.

My process is suitable for use with any of the aluminasupported platinumhydroforming catalysts described in the prior art, including unpromotedplatinum-on-alumina, as well as platinum-alumina catalysts which containa promoting additive such as vanadia, chromia, titania, iridium,rhodium, an oxide of phosphorus, or the like, or a mild crackingadjuvant, such as boria, silica, fluorine, chlorine, or the like. Thecatalysts commonly contain platinum in a proportion between 0.05 and 1percent by weight, based on dry A1 0 Third components are usuallypresent in a proportion between about 0.1 and 10% by weight.

The following specific examples will more fully illustrate my invention.

Example 1 A Mid-Continent virgin naphtha 'was subjected to aquasi-iso-thermal hydroforming operation in accordance with my newtechnique at a pressure of 300 pounds per square inch gage, an hourlyweight space velocity of 1.0,

and a hydrogen input of 5,000 standard cubic feet per barrel. Thecharging stock had an ASTM boiling range of 200 360 R, an F-l octanenumber of 44, and a sulfur content of 0.03%, and contained 41.5%naphthenes, 50% paraifins, and 8.5% aromatics. The catalyst was cogelledplatinum-on-alumina containing 0.6% by weight of platinum. During thefirst 80 hours of operation, the reaction zone was maintained at atemperature of 920 F., and the F-1 octane number of the unstabilizedreformate declined from an initial level of 98.0 to a final level of96.0, corresponding to a decline rate of 2.5 units per 100 hours. Thetemperature was thereupon raised to 955 F., where it was maintained for40 hours... During this time the octane number of the unstabilizedreformate ranged between 100.3 and 100.6 with no marked decline. At theend of this time, the temperature was lowered to 949 F. and maintainedfor 128 hours, during which time the product octane number declined froman initial level of 99.7 at the rate of 0.8 unit per 100 hours.

Example 2 A parafiinic heavy naphtha charge containing 37% parafiins,50% naphthenes, and 13% aromatics, and having a final boiling point of353 F. was subjected to hydroforming in an isothermal-type reaction zoneat a pressure of 300 pounds per square inch gage, an hourly weight spacevelocity of 1.5, and a hydrogen input rate of 5,000 standard cubic feetper barrel. The catalyst was cogelled platinum-on-alumina containing0.6% by weight of platinum. During the first 80 hours of operation, thecatalyst temperature was held at 920 F. and an unstabilized product wasobtained having an initial F-l octane number of 98.5 and declining atthe rate of 1.4 units per 100 hours. The temperature was then raised to955 F., as a result of which the octane level rose to 100.8 at 140 hourson stream and declined to only 98.3 at 376 hours on stream, equivalentto an activity decline rate of 1.0 unit per 100 hours.

While I have described my invention with reference to certain specificexamples, it is to be understood that such examples are illustrativeonly and not by way of limitation. Numerous alternative charging stocks,catalysts, manipulative steps, operating conditions, and other processdetails will be apparent from the above description to those skilled inthe art.

In accordance with the foregoing description, I claim as my invention:

1. In a method for hydroforming a petroleum naphtha in the presence ofan alumina-supported platinum catalyst at a hydroforming temperaturebetween about 875 and 1000 F. and obtaining therefrom a gasoline havingan F-l octane number above about 90, the improvement which comprisespreconditioning the said catalyst prior to said hydroforming operationby exposing the said catalyst for a period of more than about hours tocontact with a hydrocarbon stock of naphtha boiling range underhydroforming conditions, including an hourly weight space velocitybetween about 0.5 and 5.0, at a temperature from 15 to 75 F. below theinitial temperature to be employed in the ensuing hydroformingoperation, and thereafter directly raising the temperature of the saidcatalyst to said initial hydroforming level, whereby the activitymaintenance of the said catalyst in the ensuing hydroforming operationis substantially improved.

2. In a method for hydroforming a petroleum naphtha in the presence ofan alumina-supported platinum catalyst at a hydroforming temperaturesufficient to obtain therefrom a gasoline having an F-l octane numberabove about 90, the improvement which comprises preconditioning the saidcatalyst prior to said hydroforming operation by exposing the saidcatalyst for a period of more than about 10 hours to contact with apetroleum naphtha under hydroforming conditions, including an hourlyweight space velocity between about 0.5 and 5.0, at a substantiallyconstant temperature between about 800 and 950 F.

andfrom 15 to 75 F. below the initial temperature to be employed in theensuing hydroforming operation, and thereafter directly raising thetemperature of the said catalyst to said initial hydroforming level,whereby the rate of decline in activity of the said catalyst in theensuing hydroforming operation is substantially reduced.

3. In a method for hydroforming a petroleum naphtha in the presence ofan alumina-supported platinum catalyst at a hydroforming temperaturebetween about 875 and 1000 F. and obtaining therefrom a gasoline havingan F-l octane number above about 90, the improvement which comprisespreconditioning the said catalyst prior to said hydroforming operationby exposing the said catalyst for a period of more than about 10 hoursto contact with said petroleum naphtha under hydroforming conditions,including an hourly weight space velocity between about 0.5 and 5.0, ata temperature between about 800 and 950 F. and from 15 to 75 F. belowthe initial temperature to be employed in the ensuing hydroformingoperation, at which temperature a hydroformate is obtained of ananti-knock quality from 2 to 10 F-l octane units below the maximum levelafforded by the said catalyst in the ensuing hydroforming operation, andthereafter directly raising the temperature of the said catalyst to saidinitial hydroforming level, whereby the activity maintenance of the saidcatalyst in the ensuing hydroforming operation is substantiallyimproved.

4. In a method for hydroforming a petroleum naptha in the presence of analumina-supported platinum catalyst at a hydroforming temperaturebetween about 875 and 1000 F. and a pressure between about 100 and 500pounds per square inch gage and obtaining therefrom a gasoline having anF-l octane number above about 90, the improvement which comprisespreconditioning the said catalyst prior to said hydroforming operationby exposing the said catalyst for a period of around 10 to 100 hours tocontact with a petroleum naphtha under hydroforming conditions,including an hourly weight space velocity between about 0.5 and 5.0, ata pressure within the said range and at a temperature from 25 to 50 F.,below the initial temperature to be employed in the ensuing hydroformingoperation, and thereafter directly raising the temperature of the saidcatalyst to said initial hydroforming level, whereby the rate of declinein activity of the said catalyst in the ensuing hydroforming operationis substantially reduced.

5. In a method for hydroforming a petroleum naptha in the presence of analumina-supported platinum catalyst at a hydroforming temperaturebetween about 875 and 1000 F. and a pressure between about 100 and 500pounds per square inch gage and obtaining therefrom a gasoline having anF-l octane number above about 90, the improvement which comprisespreconditioning the said catalyst prior to said hydroforming operationby exposing the said catalyst for a period of around 10 to 100 hours tocontact with said petroleum naptha under hydroforming conditions,including an hourly weight space velocity between about 0.5 and 5.0, ata pressure within the said range and at a temperature from 25 to 50 F.,below the initial temperature to be employed in the ensuing hydroformingoperation, and thereafter directly raising the temperature of the saidcatalyst to said initial hydroforming level, whereby the rate of declinein activity of said catalyst in the ensuing hydroforming operation issubstantially reduced.

6. In a method for hydroforming a petroleum naptha in the presence of afixed-bed catalyst consisting essentially of alumina and between about0.05 and 1 percent by weight of platinum, based on dry A1 0 at apressure between about 100 and 500 pounds per square inch gage and ahydroforming temperature between about 875 and 1000 F. sufiicient toobtain therefrom a gasoline having an F-l octane number between aboutand 100, the improvement which comprises preconditioning the saidcatalyst prior to said hydroforming operation by exposing the saidcatalyst .for a period of between about 10 and 100 .hours to contactwith said petroleum naptha under hydroforming conditions, including anhourly weight space velocity between about 0.5 and 5.0, at a pressurewithin the said range and at a substantially constant temperature from15 to 75 F. below the initial temperature to be employed in the ensuing'hydroforming operation, and thereafter directly raising the temperatureof the said catalyst to said initial hydroforming level, whereby theactivity maintenance of the said catalyst in the ensuing hydroformingoperation is substantially improved.

7. In a method for hydroforming a naphthenic petroleum naphtha in thepresence of a fixed-bed catalyst consisting essentially of alumina andbetween about 0.05 and 1 percent by weight of platinum, based on dry A1at a pressure between about 100 and 500 pounds per square inch gage anda hydroforming temperature between about 875 and 1'000 F. sufficient toobtain therefrom a .gasoline having an F-l octane number between about90 and 100, the improvement which comprises preconditioning the saidcatalyst prior to said hydroforming operation by exposing the .saidcatalyst for a period of between about "10 and 100'hours'to contact witha hydroformed petroleum naphtha under hydroforming conditions, includingan hourly weight space velocity between about 0.5 and 5.0, at a pressurewithin the said range and at a temperature from to F. below the initialtemperature to be employed in the ensuing hydroforming operation, andthereafter directly raising the temperature of the said catalyst to saidinitial hydroforming level, whereby the activity maintenance of the saidcatalyst in the ensuing hydroforming operation is substantiallyimproved.

References Cited in the file of this patent UNITED STATES PATENTS Attesting; Officer UNITED STATES PATENT OFFICE 3 CERTIFICATE OF CORRECTIONPatent N00 2,885,351 May 5, 1959 Walker F, Johnston, Jra

It ishereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected. belowo In the grant, line 2, for "aseignor to The AmericanOil Company," read assignor to The American Oil Company, a corporationof Tera-e, g

in the heading to the printed specification, line 5, for "The American.Oil Company" read assignor to ihe American Oil Company, a corporationof Texas Signed and sealed this 29th day of mama iceoo I i m) Attest:

KARL H, AXLINE ROBERT c. WATSON Comnissioner of- Patents

1. IN A METHOD FOR HYDROFORMING A PETROLEUM NAPHTHA IN THE PRESENCE OFAN ALUMINA-SUPPORTED PLATINUM CATALYST AT A HYDROFORMING TEMPERATUREBETWEEN ABOUT 875 AND 1000* F. AND OBTAINING THEREFROM A GASOLINE HAVINGIN F-1 OCTANE NUMBER ABOVE ABOUT 90, THE IMPROVEMENT WHICH COMPRISESPRESONDITIONING THE SAID CATALYST PRIOR TO SAID HYDROFORMING OPERATIONBY EXPOSING THE SAID CATALYST FOR A PERIOD OF MORE THAN ABOUT 10 HOURSTO CONTACT WITH A HYDROCARBON STOCK OF NAPHTHA BOILING RANGE UNDERHYDROFORMING CONDITIONS, INCLUDING AN HOURLY WEIGHT SPACE VELOCITYBETWEEN ABOUT 0.5 AND 5.0, AT A TEMPERATURE FROM 1K TO 75* F. BELOW THEINITIAL TEMPERATURE TO BE EMPLOYED IN THE ENSURING HYDROFORMINGOPERATION, AND THEREAFTER DIRECTLY RAISING THE TEMPERATURE OF THE SAIDCATALYST TO SAID INITIAL HYDROFORMING LEVEL, WHEREBY THE ACTIVITYMAINTENANCE OF THE SAID CATALYST IN THE ENSUING HYDROFORMING OPERATIONIS SUBSTANIALLY IMPROVED.